In wide bandgap semiconductors such as SiC, a thickness of a drift layer for providing a certain withstanding voltage can be reduced due to its physical property. As a result, since the resistance of the drift layer can be suppressed to a low level, semiconductor devices having a low electrical loss are expected to be obtained.
Generally, a PiN diode has a p-n junction. When a forward bias is applied thereto, energy of the minority carriers exceeds the p-n junction energy, conductivity change is generated by the minority carriers, and the resistance can be lowered. In addition, as the temperature of the device increases, the energy of the minority carriers exceeding the p-n junction increases so that they can easily exceed the junction. For this reason, the voltage at the rising-edge of the I-V curve is lowered as the temperature increases.
In the case of a PiN diode using Si and having a high withstanding voltage, the thickness of the drift layer is large. Therefore, as the temperature increases, the resistance of the thick drift layer increases. Therefore, the lowered amount of the voltage at the rising-edge is offset by the increased amount of the resistance in the drift layer. Accordingly, the on-voltage in the requirement current in the vicinity of the operational temperature increases as the temperature increases.
As a result, even when diodes are used in parallel with each other in a circuit, and the electric current is concentrated on a certain device, the temperature of that device increases, and the resistance also increases, so that it is possible to alleviate the current concentration, and spontaneously suppress breakdown.
In the case of SiC, the reduction of the rising-edge voltage accompanied by the increased temperature is generated similarly to a typical Si diode. However, since the thickness of the drift layer for providing a withstanding voltage is small, the resistance in the drift layer does not increase as the temperature increases. Furthermore, the on-voltage in the requirement current in the vicinity of the operational temperature is lowered as the temperature increases.